Piston blanks



Paiented Nov. 21, 1961 3,009237 PISTON BLANKS Carl Lehmeier, 315 Sumac Laue, Santa Mnica, Cahf. Filed Jan. 25, 1954, Ser. N0. 406,007 4 Claims. (C1. 29-190) This invent-ion relates to pistons or similar objects of: cut shape having an end Wall and a skirt or cylindrical wall ortion integral therewith, and portions of which are of varying thickness for functional purposes.

Prirnarily, the invention constitutes a modification 0f and funther disclosure of piston design and punch and die construotion which may be utilized in making the pis ton blanks such as described and clairnecl in the appl-ication of Rornaine Elden Watson, John R. Boston, and Carl Lehmeier, Serial N0. 35,388, filed Inne 26, 1948, and now in issue as Patent N0. 2,667,390 dated January 26, 1954.

I have found that the die of a piston blank may aifect the flow of material frorn the blank along the surfaces o-f the die cavity and punch forming the piston blank, and :that accurate control of the height of the skirt or wall 0f the piston, panticularly where the skirt has portions of different lengths, may be related t0 corresponding modifications of the surfaces 0f the die eavity or.those of the punch, or both.

An object 0f the invention is to facilitate the flow o-f the metal by single stroke irnpact extrusion, such as described in the aforernentioned application and patent, and to prevent excessive flow above certain desired heights 0f the skirt portion, while reducing =to a minirnum the amount of material which may be required to be removed by subsequent machining of the blank for producing the finished piston.

In the joint application of the same inventors, above named Watson, Boston and Lehmeier, Serial N0. 42,935, now Patent N0. 2,756,876 is also shown an apparatus and a method is d-escribed, to which the present invention is related. In the sec0nd of said applications is partieularly pointed out and described the eifect 0f certain flow controlling bevel surfaces formed on the punch, and by which the rate at which the recesses in the punch are filled by the metal flowing upwardly along the punch, on the impact extrusion stroke, shall be at the same rate as that at which the thinner portion o-f the wall of the skir:t wal1 is moving.

The present invention is concemed with still further eontrol of metal flow, and by which the open end 0f the ski1t rnay be held -to substantially uniform height, as was done in praoticing the joint invention of the above-named applications, and in addition, -by which, where desired, the height of the skirt between the bosses may be maintained lower than the height over the bosses, to meet requirements of motor and engine manufacturers using large numbers of such pistons.

Where it is desired to maintain the interior surface of the piston substantially cylindrical and toattain the lightest possible weight of the finished piston, the die cavity may be provided with means which effect both additional 'retarding of the flow of metal from the end of the punch on the long skirt portion, which, however, leaves the exterior slightly n0n-cylindrical, and thus requires machining to a slightly greater overall depth.

As an alternative, and which may be carried out without adding materially in fa0t an extremely small amount 0f weight, if any, and yet provide for balancing the space of the flow by providing thickened skirt portions between the bosses may be by forming eccentric arcs of the oylindrieal surface 0f the inside 0f the pist0n while forming the exterior in a true cylinder and only slightly larger than the desired finished macnined piston.

In my present modification of the inventions 0f which I was a joint inventor, as appears in the applioations above identified, are illustrated in the accompanying drawings, in which:

FIGURE 1 is a plan 0f a piston blank.

FIGURE 2 is the side elevation of the same.

FIGURE 3 is an axial seotion through the wrist pin bosses.

FIGURE 4 is a similar se0tion at right angles showing the piston blank after machining to the plane 0f FIG- URE 3.

FIGURE 5 is a section through the punch and die cavity showing a slug in position to be extruded, taken on an offset plane.

FIGURE 6 is a fragmentary section through the wrist pin boss portion showing the osition of the metal when partly extruded.

FIGURE 7 is a section detail through the boss cavity portion of the punch and showing a metal flow impeding element on the die and its relation t0 the punch.

FIGURE 8 is a fragmentary horizontal section through the piston blank and the skint and one 0f the bosses showing the efie0t of this flow im-peding element.

FIGURE 9 is a plan view partially fragmentary, showing the blank With a cylindric-al exterior and thi0kened portions on the interior between the bosses.

R-eferring to the piston blank shown in FIGURES 1 to 4 and 8, the head of the piston is indicated at 1, which may be flat 0r crowned, 0r of other suitable shape on the exterior and which is shown as slightly concave on the interior. 'Ihis piston head is joined with a thiokened portion f0rming a ring flange 3 and a substantially cylindrical ski1t portion 5, With opposite wrist pin bosses 6 joining the head and extending along and integral With the skirt.

In FIGURES l, 2, 3, and 8 are shown side depressions extending circumferentially for a considerable distance around thezone 0f the bosses 6 and the exterior, and indicated by the side lines 10 and bottorn line 11, and by reason of which the Wall 112, above and each way fr0m the bosses, is somewhat thinner than the remain.ing substantially cylindrical portions of the skirt.

In FIGURE 3 it will appear that this depressed surface is shown slightly tapered, extending inwardly, as at 13, from the true cylinder indicatedby the 'broken lines 14. These opposite arcuate depressions are formed by a corresponding projeotion or pad-like protuberance 40, in the die, the lower edge of which is indicated at 41. The die :avity m-ay be cylindrical except for this protuberance.

It will be noted also that the skirt portion 5 rises slightly higher above the boss at 15, than at the depressed or scalloped portions 16 therebetween.

Bevels 17 and 18 at the base 0f the bosses are the result of bevels formed on the punch and which have a choking effect, as particulafly descri bed in said joint applioation Serial N0. 42935 now Patent N0. 2,756876.

The finished piston is, 0f course, rriachined to present a cylindrical exterior, and suitable piston ring grooves, as at 22, a're cut as shown, while the -pin bosses are bored, -as at 20, to receive the wrist'pin.

The die is shown as having a bott0m surface 30, and a cylindrical su'rfac0 31. A punch 35 has its end so formed as to shape the inner face of the piston head and, likewise, has reduced portions 36 to fonn the ring flange 3 and the boss rec'esses 38 are formed thereon in FIGURE 5. As noted, the section is taken on an offset plane throu-gh a boss cavity and a'portion of the punch between the cavities. At the recesses 38' and around the perimeter of the open end are formed bevels 42 and 43, forming the bevels 17 and 18 heretofore referred to.

Thus, as a blank B, which is shown as a substantially cylindrical billet or slug, is struck by the punch 35,

Which continues its downward movement from that shown in FIGURE 5 to that shown in FIGURE 7, the metal flows into the recesses, the ring flange and the skirt forming spaces rising along witl1 the punch at substantially the same rate during this impact extrusion operation, in the manner particularly described in application Serial N0. 42,935. There is a tendency for the material to flow |more rapidly in the zone of these bosses, however, I may avoid an excessive or abnormal flow above the sarne, by using the retarding or choking protu=berance pads 40 restrict the escape area between the punch and the wall of the die cavity.

The result is that, if desired, the height of the piston blank at the end of the stroke of the punch may be substantially even, or it may be perrnitted to flow up wardly somewhat in the high portions 15 with relation to the lower portion 16.

Obviously, this choking control may be used to cause the high portions of the piston skirt, such as a1: 15, to be forrned at any angular position with relation to the bosses, while the low portions, as at 16, would be on opposite sides of the piston between high portions.

As a modification, and for some purposes to be preferred, I may enlarge the escape area between the bosses by forrning the inner surface of the skirt eccentric between the bosses. Thus, the portions indicated at 50 may be substantially concentric with oflset axes 51, with the radius of the arc, indicated by the arrow 52, such that these eccentric surfaces menge with the thinner Portion cf the wall 55 in the zone of the bosses.

Inasmuch as the punch obviously is machined to form these inner cylindrical surfaces eccentric to the outer cylindrical surface of the piston skirt, and correspondingly with the inner surface 31 of the die cavity, this modification of the punch is not attempted to be shown.

Correspondingly, it is to be understood that the amount of difference in thickness need only be relatively very slight; for example, ranging from a sixtyfourth or less to a thirty-second, up to perhaps a sixteenth at the most, depending on the size of the piston, whereas in the drawings the contrast is exaggerated for clearness of illustration. Thus, assuming the piston blank is of approximately the size ShOWn in the drawings, the thickness of this thin 0r choked flow area would be thinner by only a small percentage, for exarnple, a wall of threesixteenths of an inch would be thinned only by a one thirty-second or three sixty-fourths of an inch. In FIG. 9, the ratio between the thickened and thinned portion is approximately as follows: The thinned portion is two-thirds of the thicker ortion between the bosses.

The billet B may be specially formed to provide more metal in line with the boss recesses of the punch. Such a billet may be preformed and of cast material, or of worked alloy, and may, if desired, contain a snbstaritial percentage of silicon; or for some pistons, any suitable alloy may be chosen. The billet may be preformed by a machine process, pre-cast, or it may be pre-hit before subjecting it to the impact extrusion stroke of the punch 35.

While a stripper die of comnron, well-known construction may be used to guide the punch into the cavity, it has been found desir-able to avoid any tendency cf the punch to become eccentric, as far as possible, and to this end, I may form a central cavity, as indicated a1; 60 in broken lines in EIGURE 5, and correspondingly, so shape the punch.

From the foregoing description it will be seen that the escape area or radial width of space, through which the metal asses between the punch surface of the die cavity, may be varied to facilitate contro1 of the flow. The oontour, whether flat or scalloped, of the top edge or open end of the piston may be forrned by the single stroke extrusion method and to substantially the precise height desired for the finished piston. Thus, machining work or grinding, if any, at the edge of the skirt is minimized, and no amount of weight of material of any consequence is wasted.

By the variation of wall thickness by eccentric cylindrical surfaces Within the skirt, the blank may be formed to a precise external diameter, only very slightly more than that of the finished machined surface fitting into the cylinder.

The invention is concerned at present with piston blanks made of aluminurn having a predetermined and desirable alloy content, and the finished piston blanks possess characteristics of great strength whereby the head and Walls may be of less thickness than pistons formed by present methods, and with resultant light weight also, as indicated in the applications referred to, superior structural strength is attained by such a method. The modifications here particularly illustrated and described are summarized in the appended claims.

I claim:

1. A piston blank comprised of a single piece of cast metal alloy containing a substantial percentage of silicon having an integral head portion, a ring flange portion, and opposite wrist pin bosses extending from the head and along fche skirt portion for a substantial distance in relation to the length of the skirt, and the skirt portion having eccentric surfaces forming radially thinner wall sections at each side of the piston and extending across and each way from the angular segmental zone of the pin bosses and to the open end of the skirt, said thinner wall section being thinner radially than that of the circumferentially intervening wall sections by an amount ranging from a sixty-fourth upto one-sixteenth of an inch.

2. The structure defined in claim 1, in Which the eccentric |thickened skirt portions are forrned on the interior by substantially cylindrical surfaces offset inwardly from parallelism with the adjacent cylindrical exterior of the skirt.

3. A piston blank composed of a single piece of cast perworked silicon containing metal alloy having an integral head portion, a thickened ring flange portion and opposite wrist pin bosses extending along the head and skirt portions for a considerable distance in relation to the length of the skirt and integral therewith, the skirt ortion having segmental areas of relatively thin radial section located on opposite sides of the piston and each being of substantially one-fourth the circumference and extending from the open end of the skirt substantially to the ring flange portion, the relatively thin radial sections being substamtially to of an inch less in radial thickness throughout the thin area than that of the adjacent thicker portions of the wall.

4. The piston blank defined in claim 3 in which the relatively thinner sections extend longitudinally fto higher points With relation to the head and form scallops on opposite sides of the open edge of the skirt.

References Cited in the file of this patent UNITED STAT ES PATENTS 1936598 Handler Nov. 28, 1933 2,080399 Deibel May 18, 1937 2333,859 Groene Nov. 9, 1943 2,344358 King Mar. 14, 1944 2368355 Guiney Jan. 30, 1945 2,411699 Somes Nov. 26, 1946 2,413,947 Boyd Jan. 7, 1947 2465,792 Davis Mar. 29 1949 2,620530 Sulprizio Dec. 9, 1952 2780-505 Veneer Feb. 5, 1957 FOREIGN PATENTS 140,211 Switzerland Aug. 16, 1920 

